Nt32Pkg/PlatformBootManagerLib: zero EFI_GRAPHICS_OUTPUT_BLT_PIXEL.Reserved

Nt32Pkg/PlatformBootManagerLib: zero EFI_GRAPHICS_OUTPUT_BLT_PIXEL.Reserved

The PlatformBootManagerWaitCallback() function sets White.Reserved to
0xFF; it should be 0x00. Also, use a more compact form to assign the
component fields.

Suggested-by: Jordan Justen <jordan.l.justen@intel.com>
Cc: Andrew Fish <afish@apple.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>